This invention relates to hybrid circuits for providing isolation between transmitting and receiving lines connected to transmitting-receiving devices. More particularly, it is concerned with active hybrid circuits for coupling between a two-wire transmitting and receiving device, such as a telephone subset, and transmitting and receiving lines.
In certain communications systems, such as conventional telephone systems, two-wire transmitting-receiving devices are employed. These devices are two terminal devices which both transmit and receive signals. In order to prevent received signals from being re-transmitted with transmitted signals an isolating arrangement is necessary. Networks of passive circuit components designated as hybrid circuits are widely employed for this purpose and are well-known in the communication art. Hybrid circuits typically employ transformers together with capacitors of fairly large value. In addition, for certain applications signal gain is needed to make up for various transmission losses; and, therefore, amplifier circuitry is also required.